The present invention relates to a method and an apparatus for a lamp anneal, and more particularly to a method and an apparatus for a lamp anneal in order to form an ohmic contact between a semiconductor wafer and a metal thin film provided on the semiconductor wafer as well as a method and an apparatus for a lamp anneal in order to activate ions implanted into a semiconductor wafer.
Lamp anneals have widely been used to form an ohmic contact between a semiconductor wafer and a metal thin film provided on the semiconductor wafer or to activate ions implanted into a semiconductor wafer without, however, any excess diffusion of the implanted ions.
As the size of the semiconductor wafer is increased, a temperature difference between a center portion and a peripheral portion of the semiconductor wafer in a lamp annealing process is likely to be increased. In Japanese Laid-open Patent Publication No. 61-198735, there is disclosed a lamp anneal, wherein a plurality of ring-shaped lamps are co-axially aligned and provided over the semiconductor wafer and also a plurality of temperature sensors are provided at a center portion of the semiconductor wafer and peripheral portions thereof, in addition intermediate portions between the center portion and the peripheral portions so as to individually detect temperatures of the center portion, the intermediate portions and the peripheral portions of the wafer, whereby power to be supplied to the individual co-axially aligned and ring-shaped lamps is independently controlled based upon signals indicating the detected individual temperatures.
Since, however, a stage for holding the wafer is normal stage, it is required to attach a plurality of the temperature sensors onto a surface of the wafer each time the wafer on the stage is replaced.
If contact temperature sensors are attached onto the surface of the wafer, this raises problems with both deterioration in workability due to complicated operations or works for attachment of the contact temperature sensors and variation in position of the attached contact temperature sensors over the surface of the wafer. Further, another problem is raised with a possibility of damaging semiconductor devices integrated on the wafer due to contact between the contact temperature sensors and the semiconductor devices.
Since, further, the contact temperature sensors are attached onto the wafer surface which faces the lamps to be used for annealing, the attached contact temperature sensors are thus exposed directly to radiation from the lamps, thereby making it difficult for the contact temperature sensors to detect temperatures accurately.
On the other hand, if a plurality of radiation thermometers as temperature sensors are provided on the wafer surface, then a large area or a large space is required thereby making it difficult to monitor plural positions of the wafer surface. These radiation thermometers do not conduct a direct measurement of the temperature of the wafer, for which reason values indicated by the radiation thermometers may be varied dependent upon the surface state of the wafer. This means it difficult for the radiation thermometers to detect accurately the actual temperature of the wafer for power control of the lamps.
A susceptor may be used for subjecting a large size wafer such as 8-inches wafer to an anneal for formation of an ohmic contact or an activation of ions implanted. In this case, it may be required to conduct different controls in a direction along which the susceptor is carried into or out in view of relationships between the center and peripheral portions of the wafer. The above co-axial alignment of the ring-shaped lamps is incapable of conducting the different controls in the direction along which the susceptor is put into or out.
In the above circumstances, it had been required to develop a novel method and apparatus for a lamp anneal free from the above problems.
Accordingly, it is an object of the present invention to provide a novel apparatus for a lamp anneal free from the above problems.
It is a further object of the present invention to provide a novel apparatus for a lamp anneal capable of improvement in workability.
It is a still further object of the present invention to provide a novel apparatus for a lamp anneal capable of accurately detecting temperatures of various points of the wafer for realizing a uniformity in temperature over the wafer.
It is yet a further object of the present invention to provide a novel method for a lamp anneal free from the above problems.
It is furthermore an object of the present invention to provide a novel method for a lamp anneal capable of accurate control of power to be supplied to individual positions of a large size wafer.
The present invention provides a lamp anneal apparatus comprising: a chamber; a wafer holder accommodated in the chamber for holding a wafer to be annealed; a first set of lamps provided over a top wall of the chamber; and a second set of lamps provided under a bottom wall of the chamber, wherein the wafer holder has a plurality of contact temperature sensors which are positioned under the wafer so that the contact temperature sensors receive substantially no radiation from lamps, and the contact temperature sensors are in contact with a bottom surface of the wafer for supporting all of the wafer""s weight and detecting temperatures at different points of the wafer.
The above and other objects, features and advantages of the present invention will be apparent from the following descriptions.